Neopentyl glycol esters



United States Patent Ohtice 3,048,608 Patented Aug. 7, 1962 Thisinvention relates to novel synthetic lubricating compositions andparticularly to synthetic lubricating compositions which haveoutstanding lubricating characteristics at both high temperatures andlow temperatures.

This application is a continuation-in-part of our copending applicationSerial No. 713,801, which was filed on February 7, 1958.

With the development of aircraft engines that operate at peak efficiencyat extremely high altitudes there has arisen the need to providelubricants suitable for use in these engines. These lubricants must havea combination of properties not possessed by conventional lubricants:they must remain effective over a wide range of temperatures, they musthave good oxidation and thermal stability in order that they may retaintheir useful properties after operation for long periods of time at hightemperatures, they must have low pour points so that they may func-.tion at low temperatures and they must have high flash points to avoidrisk of fire during high temperature operation.

The conventional mineral oil lubricants have been found to beunsatisfactory for use in modern aircraft engines. Those mineral oilsthat have satisfactory low temperature viscosities generally have flashpoints that are dangerously low and high temperature viscosities thatare insufiicient to provide the required lubricity, whereas thosemineral oils that have satisfactory properties at elevated temperaturesare too viscous for use at low temperatures. The incorporation of theusual lubricant additives does not overcome the deficiencies of themineral oils as lubricants for jet aircraft engines.

Esters prepared from a wide variety of monohydric or dihydric alcoholsand monocarboxylic or dicarboxylic acids have been suggested aslubricants. While they provide an improvement over the mineral oillubricants, these esters do not, in general, have the combination ofhigh temperature and low temperature properties that are essential inlubricants for jet aircraft engines.

We have discovered a new class of compounds that are useful aslubricating compositions and which possess properties which are superiorto those of lubricating compositions of the art. The present compoundsexhibit surprising stability and other desirable properties at elevatedtemperatures and also excellent properties at low temperatures. Thiscombination of properties makes them valuable as lubricants for jetaircraft engine.

The compounds of the present invention are diesters of dicarboxylicacids which are fully esterified'with a neopentyl glycol, the hydroxylgroup in the alcohol not esterified with the dibasic acid beingesterified with a monocarboxylic acid. These compounds may also be considered to be esters of a dicarboxylic acid esterified with two molesper mole of acid of a mono ester of a neopentyl alcohol and amonocarboxylic acid. These esters have the structural formula wherein-OOC-R-COO represents a dicarboxylic acid radical, R represents aneopentyl glycol radical in which the hydroxyl group has been replacedby an acid radical, and R represents a neopentyl glycol radical, aneopentyl trihydric alcohol radical, or a neopentyl tetrahydric alcoholradical in which all of the hydroxyl groups have been replaced by acidradicals or by acid and alkoxy radicals.

The neopentyl alcohols used in the preparation of the novel esters ofthis invention are those compounds which contain a neopentyl nucleus andwhich contain two or more hydroxyl groups. These alcohols have thestructural formula HOCHr-GHzOH When the alcohol is a neopentyl glycol, Aand A each represents H, Cl Br, an alkyl group containing 1 to 4 carbonatoms, or an alkoxy radical containing 1 to 5 carbon atoms. In each caseA, and A may have the same value, or they may have different values.Illustrative of these neopentyl glycols are2,2-dimethyl-l,3-propanediol, which is also known as neopentyl glycol;2- ethyl-Z-butyl-l,3-propanediol; 2,2-bis(chloromethyl)-1,3-propanediol; 2meth.yl-2-chloromethyl 1,3-propanediol; and2,2-bis(ethoxy1nethyl) l ,3 -propanediol.

When a trihydric neopentyl alcohol is used, A in the foregoing formularepresents a hydroxyl group; when a tetrahydric neopentyl alcohol isused, both A, and A represent hydroxyl groups. Illustrative of thesepolyhydric neopentyl alcohols are pentaerythritol, pentaerythritolmonomethyl ether, pentaerythritol monochloride, trimethylolethane,trimethylolpropane, and trimethylolbutane.

In order to obtain the novel esters of this invention it is necessarythat at least one mole and not more than about two moles of a neopentylglycol be used for each mole of dicarboxylic acid. When less than twomoles of the neopentyl glycol is used for each mole of dicarboxylicacid, a trihydric or tetrahydric alcohol in an amount that is thedifference between the amount of the neopentyl glycol used and two molesis used to complete the esterification of the dibasic acid.

The dibasic acids which may be used are saturated aliphatic dicarboxylicacids and aromatic dicarboxylic acids. Included among these aliphaticacids are acids having a straight chain, branched chain, or cyclizedchain and containing from 2 to 36 carbon atoms. Illustrative of theseacids are oxalic acid, adipic acid, suberic acid, sebacic acid,dodeca-nedicarboxylic acid and eicosanedicarboxylic acid. Ether acids,such as diglycolic acid, and dimerized fatty acids may also he used.Among the aromatic dicarboxylic acids that may be used are thefollowing: phthalic acid, terephthalic acid, isophthalic acid,naphthalene 1,5-dicarboxylic acid, and methylene bis benzoic acid. Ifdesired, a mixture of two or more of the dicarboxylic acids may be used.It is to be understood that the term dicarboxylic acids as used hereinincludes the anhydrides of these acids.

The monocarboxylic acids which are used in the esterification aregenerally saturated aliphatic monocarboxylic acids containing from 2 to22 carbon atoms, preferably from 4 to 18 carbon atoms. These acids mayhave straight chains or branched chains and may contain an alicyclicgroup or an aryl substituent. Among these acids are butyric acid,caproic acid, caprylic acid, Z-ethylhexanoic acid, pelargonic acid,lauric acid, palmetic acid, stearic acid, arachidic acid, behenic acid,and phenylacetic acid. Mononuclear aromatic acids, such as benzoic acid,toluic acid, and p-t-butvlbenzoic acid, may also be used. A

single monocarboxylic acid or a mixture of two or more of these acidsmay be used in the preparation of the esters.

3 The novel esters may be represented by the structural formula In thisformula A and A may be the same or different and each represents H, analkyl group containing from 1 to 4 carbon atoms, Cl, Br, or an alkoxyradical containing 1 to 5 carbon atoms; A and A, may be the same ordifferent and each represents H, an alkyl group containing from 1 to 4carbon atoms, Cl, Br, an alkoxy goup containing 1 to 5 carbon atoms, asaturated aliphatic acid radical containing 2 to 22 carbon atoms, or amononuclear aromatic acid radical. Z and Z may be the same or differentand each represents a saturated aliphatic acid radical containing 2 to22 carbon atoms or a mononuclear aromatic acid radical. R represents theresidue of a saturated aliphatic dicarboxylic acid containing from 2 to36 carbon atoms or the residue of an aromatic dicarboxylic acid.Illustrative of these novel esters are the following:

(1) Di(neopentyl glycol monopelargonate)azelate CH3 CH3 1111080 0 OH2(J-CHaO 0 0 (011910 0 O OHz-iJ-OHzO 0 0 H" CHa JHQ (2) Di(neopentylglycol monocaproate) adipate CH3 CHa 1 11.050 0 o 0112 0431110 0 0(011;)40 o 0 CHF-CHQO 0 0 0 H" lHa JHs (3) (Trimethylolpropanedivalerate) (neopentyl glycol monovalerate) azelate CH3 CH2OOCC4H9 HrCiOO O OH2( )CHzO O C (0111010 0 O OHr-C-CHrO O C C-tHB JHa (E2115 (4)(Pentaerythritol tricaproate) (neopentyl glycol monopelargonate)phthalate r H17C3COOCH2CCH2OOC I 01120 0 0 6 H CH3 4:

COOCH3- CH2O O C 05H" 5 (Trimethylolethane dil aurate) (2methyl-2-butyl-1, 3

propanediol monobutyrate) sebacate CH5 CH3 H1030 0 o 0H2( 10Hr0 0 0(0H,)t0 o 0 0Hl( 3-0H20 o 0 0 11123 liHg CHzO 0 00111123 (6) Di(neopentyl glycol monocaproate) diglycolate CH3 CH3 H11C OOOCHr CCH O 0001120 01120 0 0011 -0011 0 000 111 CH3 H3 (7) (Pentaerythritolmonomethyl ether dipelargonate) (neopentyl glycol monovalerate)succinate The novel esters of this invention may be prepared by any ofseveral possible methods. For example, the neopentyl alcohol or alcoholsmay be esterified first with the dicarboxylic acid and then with themonocarboxyl-ic acid; all of the reactants may be mixed together andthen heated to form the ester; or the neopentyl alcohol component may beesterified with one or more monocarboxylic acids so as to form apartially esterified product which contains an average of one hydroxylgroup per molecule, the partially esterified product subsequently beingesterified with dicarboxylic acid. The conditions under which theesterification is carried out are not critical. Conventionalesterification procedures are generally employed; for example, theesterification may be carried out at a temperature between and 180 C. inthe presence of an inert solvent and in the presence or absence of anesterification catalyst. The crude product of the esterification may bepurified by conventional procedures; for example, unreacted acid may beremoved by washing with alkali and volatile impurities by distillation.

The following examples illustrate this invention:

EXAMPLE I Di(Ne0pentyl Glycol Mo nopelargonate) Azelate A mixture of333.3 grams (2 moles) of neopentyl glycol, 503.3 grams (2 moles) ofpelargonic acid, 4.19 grams of phosphoric acid, 22.9 grams of activatedcarbon, and 114 grams of xylene was placed in a flask equipped with athermometer, an agitator, and a Dean-Stark water trap surmounted by areflex condenser. The mixture was heated with agitation at l60-l76 C.for 5 hours and then cooled to room temperature. Azelaic acid (301.2grams, 1 mole) and phosphoric acid (7.22 grams) were added, and thereaction mixture was heated at 170176 C. for about 5 hours. At the endof this time the ester had an acid number of 18.4. An additional 50.3grams of pelargonic acid was added and the esterification was continuedat 17618l C. for 6.5 hours. The crude product was sparged with carbondioxide to drive 01f the xylene and then filtered to remove the carbon.After dilution with an equal weight of petroleum ether, the ester waswashed with sufficient methanolic sodium hydroxide solution toneutralize the unreacted acid and then with methanolic sodium chloridesolution. About 2% by weight of activated carbon was added to the washedester. The ester was then heated at about 40 C. at about 20 mm. absolutepressure and then at about C. at 2 mm. absolute pressure to remove thepetroleum ether, water, and any other low boiling materials that werepresent. The residue was cooled to 100 C. and filtered. The esterprepared by this procedure had the following properties:

EXAMPLE II Di(Neopentyl Glycol Monovalerate) Azelate A mixture of 333.3grams (2 moles) of neopentyl glycol, 301.2 grams '(1 mole) of azelaicacid, 100 grams of xylene, 4 grams of phosphoric acid, and 22.9 grams ofactivated carbon was heated at reflux temperature for about 5 hours.Then 204.3 grams (2 moles) of valeric acid and 9 grams of phosphoricacid were added and the heating was continued until the calculatedamount of water of esterification had been collected. The crude ester soformed was purified by the procedure described in Example I. Thepurified ester had the following properties:

Acid number 0.04 Hydroxyl content percent 0.13 Saponification value424.8 Pour point F 40 Flash point F 423 Fire point F 486 EXAMPLE IIIDi(Ne0pentyl Glycol M onocaproate) Diglycolate This ester was preparedby the reaction of 2 moles of neopentyl glycol, 2 moles of caproic acid,and 1 mole of diglycolic acid according to the procedure described inExample I. After purification, this ester had the following properties:

Acid number 0.02

Hydroxyl content percent 0.95

Saponification value 411.2

Pour point F 60 Flash point F 361 Fire point F 370 EXAMPLE IV Di(Neopentyl Glycol Monocaproate) Adipate This ester was prepared by thereaction of 2 moles of neopentyl glycol, 2 moles of caproic acid, and 1mole of adipic acid according to the procedure described in Example I.After purification, this ester had the following properties:

Acid number 0.15

Hydroxyl content percent 0.08

Saponification value 434.5

Pour point F 52 Flash point F 392 Fire point F 423 EXAMPLE V (NeopentylGlycol Monovalerate) (T rimethylolpropane Divalerate) Adipale This esterwas prepared by the reaction of 1 mole of neopentyl glycol, 1 mole oftrimethylolpropane, 3 moles of Valerie acid, and 1 mole of adipic acidaccording to the procedure described in Example I. After purification,this had the following properties:

Acid number 0.01 Hydroxyl content percent-.. 0.08 Saponification value467.5 Pour point F 42 The novel esters of this invention arecharacterized by high viscosity indices; that is, their viscositiesundergo relatively little change over a wide temperature range. Inaddition these esters have excellent low temperature properties. Theseproperties combine to make the esters useful as lubricants for modernaircraft engines.

Each of the esters herein described or combinations of these esters maybe used directly as lubricants, or they may be blended with othermaterials, such as mineral oil, to obtain many combinations havingspecial characteristics. It may also be desirable to add to these esterscertain of the well-known lubricant adjuvants. For example,antioxidants, such as phenyl a-naphthylamine, 2,2 -dipyridylamine, orphenothiazine, may be present in the lubricating compositions. Theamount of antioxidant used in each case is dependent upon the specificester used and upon the choice of antioxidant. Generally about 0.5% toabout 5% by weight of antioxidant is used. Viscosity index improvers,pour point depressants, detergents, and corrosion inhibitors may also beincorporated into these compositions to improve their properties. It isto be understood, however, that the lubricating compositions of thepresent invention contain a major amount of aforedescribed novel estersand a minor amount of one or more of the lubricant adjuvants.

While the present lubricating compositions are particularly useful aslubricants for jet aircraft engines, it is to be understood that theycan also be employed as high temperature or extreme pressure lubricantsfor other equipment such as valves, gear boxes, pumps, and transmissionbelting where the lubricant i interposed between relatively moving metalsurfaces.

We claim:

1. An ester represented by the structural formula wherein Z and Z eachrepresents a member selected from the group consisting of a saturatedaliphatic monocarboxylic acid radical containing from 2 to 22 carbonatoms and a mononuclear aromatic monocarboxylic acid radical; and Rrepresents a member selected from the group consisting of the residue ofa saturated aliphatic dicarboxylic acid containing from 2 to 36 carbonatoms and the residue of an aromatic dicarboxylic acid.

2. Di(neopentyl glycol monopelargonate) azelate.

3. Di(neopenty1 glycol monovalerate) azelate.

4. (Neopentyl glycol monovalerate) (trimethylolpropane divalerate)adipate.

References Cited in the file of this patent UNITED STATES PATENTS1,975,246 Zwilgmeyer Oct. 2, 1934 2,023,976 Roberts Dec. 10, 19352,469,371 Colbeth May 10, 1949 2,499,984 Beavers et al. Mar. 7, 19502,588,194 Arundale -2 Mar. 4, 1952 2,755,250 Watson et al. July 17, 19562,820,014 Hartley et al. Jan. 14, 1958 2,837,562 Matuszak et al June 3,1958 2,862,961 Goreau Dec. 2, 1958 2,870,044 Blatz Jan. 20, 19592,891,919 Christenson et al. June 23, 1959 2,907,736 Greenlee Oct. 6,1959

1. AN ESTER REPRESENTED BY THE STRUCTURAL FORMULA